1. Field of the Invention
The present invention relates in general to a pneumatic power brake system which permits the driver to easily brake vehicle by exerting only a little pressure on the brake pedal, and more particularly to a pressure control device of the pneumatic power brake system, by which the pressure applied to the work chamber of a brake booster is suitably controlled in accordance with a brake pedal force applied to an input means of the booster from the brake pedal by the driver.
2. Description of a Prior Art
Japanese Patent First Provisional Publication No. 58-188746 shows a pneumatic brake booster equipped with an electronic pressure control means by which the multiplied pressure produced by the booster is electronically controlled in accordance with a brake pedal force applied to an input means of the booster from the brake pedal by the driver. Since the output characteristic of the brake booster can be easily changed by adjusting only the pressure control means, the brake boosters of this type are widely applicable to various brake systems. That is, if desired, it is possible to adjust the output characteristic of the brake booster according to the preference of the driver. Furthermore, when information regarding vehicle weight and vehicle deceleration and the like are electronically communicated to the pressure control means, it becomes possible to obtain ideal brake pressure which is adjustable in accordance with the operational condition of the vehicle.
However, the above-mentioned conventional brake system is somewhat slowly in producing stable multiplied brake pressure due to the inherent construction of the pressure control means.